Cobalt carbonyl is widely used commercially as a catalyst in the oxo process wherein olefins react with carbon monoxide and hydrogen to give aldehyde and alcohols. Cobalt carbonyl is also known to serve as catalyst for the reaction of methanol to give two-carbon molecules such as ethanol, acetaldehyde, and methyl acetate. See Science, Vol. 113, page 206 (1951).
The separation of cobalt catalysts from the product of oxo reactions in a form suitable for recycle is usually performed by extraction techniques, which frequently rely upon converting the cobalt catalyst to a water soluble form and then using aqueous extraction for removal from the organic product. In the carbonylation of methanol, such a procedure is not feasible as both methanol and the products are miscible with water. On the other hand direct distillation of the reaction product has the disadvantage that the cobalt catalyst is volatile and unstable and converted to forms which precipitate, coating the distillation equipment with a solid, making recycle impractical. The occurrence of cobalt (II) acetate is also observed, resulting from oxidation of cobalt carbonyl, and the cobalt (II) acetate can precipitate from the distillation heel.
Ethanol, of course, is a material of many known uses. It has recently been proposed that methanol can serve as a starting material for ethylene, being converted to ethanol by reaction with synthesis gas overcobalt catalyst, and subsequently dehydrated to ethylene. The other products of the carbonylation, methyl acetate and acetaldehyde and its acetals, also have recognized uses.